docs: def losses_by_tag(dstore, tag):
      """
      Statistical average losses by tag. For instance call
  
      $ oq extract losses_by_tag/occupancy
      """
      dt = [(tag, vstr)] + dstore['oqparam'].loss_dt_list()
      aids = dstore['assetcol/array'][tag]
      dset, stats = _get(dstore, 'avg_losses')
      arr = dset.value
      tagvalues = dstore['assetcol/tagcol/' + tag][1:]  # except tagvalue="?"
      for s, stat in enumerate(stats):
          out = numpy.zeros(len(tagvalues), dt)
          for li, (lt, lt_dt) in enumerate(dt[1:]):
              for i, tagvalue in enumerate(tagvalues):
                  out[i][tag] = tagvalue
                  counts = arr[aids == i + 1, s, li].sum()
                  if counts:
                      out[i][lt] = counts
          yield stat, out